A. Field of Invention
The present invention includes a method and apparatus for nucleated forming of metallic alloys, representing an improvement over prior art related to nucleated casting of similar materials. "Nucleated casting" is the process of spray casting molten metallic alloys in a controlled manner to form a semi-solid metallic alloy mixture with a uniform degenerative dendritic globule structure that solidifies into billet, rods or strips. "Nucleated forming" is the process of forming by die casting or die forging semi-solid nucleated cast metallic alloy mixture into molded parts.
B. Description of the Related Art
U.S. Pat. No. 5,381,847 (Ashok) for a Vertical Casting Process discloses a method for casting molten metallic alloys by spraying liquid alloys through a disruption site to atomize the liquid in a nonreactive gas environment and form droplets of alloy that solidify within a mold. This process called "nucleated casting" results in solidified alloys that possess a uniform, nondendritic structure. Ashok discloses and claims the method for nucleated casting whereby the partially solidified droplets are collected and solidified in a mold, but it does not anticipate immediately transferring a formed semi-solid mass under pressure into a die while in a semi-solid state. The current method and apparatus represent an improvement of the Ashok patent.
Ashok discloses a casting apparatus, including a molten metal source which may be a transfer lauder, conduit or other means known in the art. As disclosed, a disruption site is positioned to receive a stream of molten metal of a desired composition and convert that stream into a plurality of molten metal droplets. To prevent the droplets from oxidizing, or with aluminum alloys or magnesium, becoming a fire hazard, Ashok teaches that the molten metal source delivers the stream of molten metal to the disruption site in a controlled atmosphere. Ashok teaches that the controlled atmosphere may be any gas or combination of gases that does not react with the molten metal stream, although generally any noble gas or nitrogen is suitable. Other than alloys prone to excessive nitriding, nitrogen is preferred due to its low cost. When the molten metal stream is a copper based alloy, preferred controlled atmospheres are nitrogen, argon and mixtures thereof When the molten stream is a nickel-based alloy or a steel, the preferred controlled atmospheres are nitrogen or argon.
Ashok discloses methods for disruption of the stream of liquid metal alloy to form the atomized spray of metal, including gas atomization, magnetohydrodynamic atomization and mechanical type atomizers such as disclosed in U.S. Pat. No. 4,977,950 (Muench).
Ashok teaches that the droplets of molten metal are sprayed downward through a cooling zone in the shape of a diverging cone. The length of the cooling zone is determined to insure that an average droplet upon impact is at the required percentage of solid phase (generally five to 40 percent, and most preferably, from about 15-30 percent). Ashok also discloses that if the diameter of the mold is large, a plurality of disruption sites should be provided. The Ashok specification is incorporated herein by reference.
Ashok suggests that the process disclosed could be used for casting billets, rods and thin strips. Ashok does not teach the immediate use of the billet for die casting or die forging while the nucleated material is in a semi-solid state.
U.S. Pat. No. 3,826,301 (Brooks '301) discloses a method and apparatus for manufacturing shaped precision articles from molten metals or molten metal alloys, comprising directing an atomised stream of molten metal or molten metal alloy at a collecting surface to form a solid deposit, and working the deposit by means of a die to form a precision metal or metal alloy article. The deposit may be worked by a die pressing the deposit against the collecting surface, and the collecting surface may be a second die. Brooks '301 also discloses the metal may be sprayed into a container and then forced through a die in the bottom of the container for extrusion or, alternatively, through a shaped orifice in the ram for indirect extrusion.
U.S. Pat. No. 3,909,921 (Brooks '921) is a continuation-in-part of Brooks '301. Brooks '921 discloses that the hot deposit can be removed from the collection die by means of an ejector and transferred directly to the bottom die of a drop-forging hammer for forging. It states alternatively that the deposit may be forged at a later time either with or without the addition of heat to produce a shaped and forged article.
Neither Brooks '301 nor Brooks '921 discloses the formation of an intermediate shot or slug in a container that is then die cast. Brooks '301 claims both a method and apparatus whereby the deposit is worked on the collecting surface. Brooks '921 teaches that the hot metal particles are directed at the collecting surface or die and then forged, either directly on the surface or in a forging die.
U.S. Pat. No. 4,088,178 (Ueno) discloses a vertical die casting machine in which molten metal contained in a vertical casting sleeve located beneath a stationary platen is forced upward into the die cavity. In one embodiment, the casting sleeve is tilted for filling purposes and then moved to the vertical position for casting. This patent teaches a mechanism for tilting the container from a filling position to a casting position. See FIG. 3. Another embodiment of Ueno discloses a horizontal transport mechanism. See FIG. 4.